<!--
背景属性:

background-color: 设置背景颜色
background-image: 设置背景图片
background-repeat: 设置背景图片是否重复
background-position: 设置背景图片的位置
background-size: 设置背景图片的尺寸 
background参数: auto, cover, contain, lengrh, percentage
background-attachment: 设置背景图片是否固定
示例:

<!DOCTYPE html>
<html>
<head>
	<title>背景属性</title>
	<style>
		.box {
			width: 200px;
			height: 200px;
			background-color: #f00; 
			background-image: url("bg.jpg");
			background-repeat: no-repeat;
			background-position: center;
			background-size: cover;
			background-attachment: fixed;
		}
	</style>
</head>
<body>
	<div class="box"></div>
</body>
</html>
-->